Alain throws a stone off a bridge into a river below. The stone's height (in meters above the water), $x$ seconds after Alain threw it, is modeled by: $h(x)=-5x^2+10x+15$ What is the height of the stone at the time it is thrown?
Solution: The height of the stone at the time it is thrown is given by $h(0)$. $\begin{aligned} h( 0)&=-5( 0)^2+10( 0)+15 \\\\ &=0+0+15 \\\\ &=15 \end{aligned}$ In conclusion, the height of the stone at the time of throwing is $15$ meters.